The field of the invention is x-ray imaging systems in which an image is produced by an array of detectors.
Conventional fluoroscopy systems include an x-ray source that projects an x-ray beam through a subject such as a medical patient. An image intensifier converts the x-rays into a visible light image and a video camera is used to produce an analog video signal for displaying the image on a monitor.
Recently, high resolution solid state x-ray detectors have been developed which include thousands of photo detector elements arranged in a two-dimensional array. Each detector element produces an electrical signal which corresponds to the brightness of a picture element in the x-ray image projected by the detector. The signal from each detector element is read out individually and digitized for further image processing, storage and display. Such systems are described for example in U.S. Pat. Nos. 4,996,413; 5,352,884and 5,401,668.
As shown in FIG. 1, detector arrays are arranged in a two-dimensional array of detector elements comprised of vertical columns and horizontal rows. Each column of detector elements is connected to a single preamplifier and each row of detector elements is connected to a single control line from a row gate control circuit. The detector signals are scanned, one row at a time by sequentially enabling the row gate control lines.
As shown in FIG. 2, the result of this prior art scanning technique is that the detector signals are read out from detector regions that are equal in size and are shaped as a single horizontal line of detector elements. While this prior art technique simplifies construction of the detector array and associated circuitry, the line-shaped regions are very limiting and can have no relation to the subject matter being imaged.
Another characteristic of prior detector arrays is that they have a single, fixed image resolution. A separate signal is read from each detector element and the image resolution is, therefore, determined by the size and spacing of the detector elements. The number of rows and columns in a detector array is usually limited by economic considerations and, therefore, image resolution is usually determined by cost factors and the specified overall size of the detector array.
Another characteristic of prior detector arrays is that the detector elements are scanned at the same rate. That is, when the detector signals are scanned to refresh the displayed image, all the detector elements are scanned and their signals used to produce the next image frame. Since the detector elements accumulate charge proportional to the intensity of impinging x-rays, the detector elements in regions outside the patient will rapidly become saturated and detector elements in regions inside the patient will charge at slower rates dependent on the amount of x-ray attenuation. The x-ray dose and the time interval between scans of the detector array are set such that sufficient charge is accumulated in detectors located in regions of clinical interest. This is necessary to maintain the signal-to-noise ratio of the image at a clinically acceptable level. On the other hand, detector elements located outside the patient receive unattenuated x-rays and can become saturated, or overcharged. Since the rate at which the detector array is scanned may only be set to a single value, that value is usually dictated by the need to avoid saturation at all locations in the image.
The present invention is an improved x-ray detector having an array of detector elements which are segmented into regions, each region containing a plurality of detector elements arranged in a plurality of rows and a plurality of columns, and in which all the detector elements in a region are connected to a common data line and each detector element in a region is connected to a separate one of a plurality of control lines. A scan sequencer drives each of the control lines and may be operated to scan the x-ray detector in a variety of different ways. The detector array can be scanned to enable different scan rates in each region, to enable different resolutions in each region and to reduce the production of unnecessary data.